An audio signal may comprise one or more regions of relatively rapid change in spectral content, such as without limitation a transient audio event. Such regions of relatively rapid change may occur across a broad spectrum or within a more narrow range of frequencies. The perceptual experience of one listening to an audio signal may be affected by the manner in which such regions of the signal are rendered. For example, a listener may perceive an audio signal in which such rapid changes in spectral content are emphasized or enhanced as being more “edgy” or “crisp”. By contrast, one may perceive an audio signal in which such rapid changes in spectral content have been smoothed or otherwise de-emphasized as being more “warm” or “smooth”. Different listeners may have different preferences regarding how “edgy” or “smooth” a particular audio signal is rendered.
An analogy can be made to a visual image. In a visual image, the feature analogous to a region of rapid change in spectral content is a line defining a boundary between a region of one color and a region of a second, contrasting color. Visual image processing techniques are known to “soften” or “blur”, or conversely to “sharpen”, such transitions, as desired, in order to enhance the perceptual experience of a viewer in a desired manner.
Typical prior art static equalization techniques are not fully satisfactory for this purpose, as they do not respond dynamically to the audio signal being processed and may not as a result provide the desired listening experience for a given signal.
Therefore, there is a need for a way to process an audio signal to either smooth or enhance rapid changes in spectral content to provide a desired perceptual experience with respect to such changes.